Faster ablative Kelvin–Helmholtz instability growth in a magnetic field

Abstract

Shear flows along a plasma interface will quickly grow unstable due to the Kelvin–Helmholtz instability. If there is a concurrent temperature gradient across the interface, higher modes are stabilized by the thermal diffusion. These ablative effects must be considered in, for example, jet features in inertial confinement fusion hot-spots, or plasma plumes in young supernovae. We show that magnetization of the plasma can greatly affect the instability, even if magnetic pressure is small. This is because electrons are localized by their gyromotion, reducing the heat flux and material ablation. We use a two-dimensional numerical extended-magnetohydrodynamics approach to assess this effect for dense fusion conditions. In comparison with the unmagnetized case, self-generated Biermann fields make only a minor difference to growth rates. However, simulations with a large 50 kT external field found that the growth rate of the least stable mode increased by 40%. This has implications for mix processes in Z-pinches and magnetized inertial confinement fusion concepts.

Proton imaging of high-energy-density laboratory plasmas

“…Proton imaging, as opposed to x-ray imaging, is uniquely suited to observe the electromagnetic fields in these HED experiments and has been employed with some success to date. These self-generated fields, as well as applied fields, can change the plasma properties and can be crucial to understanding the evolution of instabilities like RT (Srinivasan, Dimonte, and Tang, 2012;Modica, Plewa, and Zhiglo, 2013;Song and Srinivasan, 2020), ablative RT (García-Rubio et al, 2021), RM (Samtaney, 2003;Shen et al, 2019Shen et al, , 2020, and KH (Ryu, Jones, and Frank, 2000;Modestov et al, 2014;Sadler et al, 2022), along with a newly discovered composition instability (Sadler, Li, and Flippo, 2020). This includes the possibility of stabilizing these instabilities or curtailing their growth with external fields (Rosensweig, 1979;Sano, Inoue, and Nishihara, 2013;Srinivasan and Tang, 2013;Praturi and Girimaji, 2019).…”

“…26(f) and 27(g)] with either transverse (Gao et al, 2012) or longitudinal (Gao et al, 2013) proton imaging of CH targets. More recent experiments have attempted to look at the self-generated magnetic fields inside denser HED shock-tube targets, where Coulomb scattering is an issue (Lu et al, 2020) and where the fields can change the heat flow in these targets, thereby changing the instability growth (Sadler et al, 2022).…”